Catalysts for hydrogen production for low temperature fuel cells by steam reforming and autothermal reforming of alcohols

ABSTRACT

The present invention involves the use of the cerium oxide based catalysts with or without 0.5-10 wt % of alkaline and alkaline earth promoters (Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra) and mixed oxides containing ceria and zirconia and/or yttria an/or lanthanide elements (Ce x M 1-x O 2 ; M=Zr, Y, La, Pr, Nd, Pm, Sm, Eu and 0.1&lt;x&lt;0.9) on the steam reforming and autothermal reforming at low temperatures of alcohols, in particular ethanol, or a mixture of these alcohols, like, for example, bio-ethanol. Low temperature was defined as 723-823 K. The catalysts of this invention exhibit good activity and stability, high selectivity to hydrogen, low formation of carbon monoxide (&lt;150 ppm), small amounts of acetaldehyde and ethene and no production of ketone.

FIELD OF THE INVENTION

This invention comprises the use of the cerium oxide based catalystswith or without alkaline and alkaline earth promoters and mixed oxidescontaining ceria and zirconia and/or elements of lanthanide group in thesteam reforming and autothermal reforming at low temperatures ofalcohols, in particular ethanol, or a mixture of these alcohols, like,for example, bio-ethanol. These catalysts presented high activity, highstability and high selectivity to hydrogen (without significantformation of CO) in the reactions described above.

Nowadays, hydrogen has been proposed as a major energy source that couldcontribute to the reduction of global dependence on fossil fuels,greenhouse gas emissions and atmospheric pollution.

Hydrogen-powered fuel cells represent a radically different approach toenergy conversion. These systems directly convert chemical energy intoelectric power, without the intermediate production of mechanical work,and they are more efficient than the conventional combustion engines[Amphlett et al, Int J. Hydrogen Energy 19 (1994) 131; Hirschenhofer etah, Fuel Cell Handbook, 1998]. There are several types of fuel cellswhich differ in the type of electrolyte and in the temperature ofoperation. Proton exchange membranes fuel cells (PEMFC) operate at lowtemperatures (˜373 K) and offer large power density along with fastresponse times [Hirschenhofer et ah, Fuel Cell Handbook, 1998].

Hydrogen for fuel cells can be derived from a variety of energy sourcessuch as gasoline, diesel, LPG, methane, and alcohols, in particularethanol. For example, the bio-ethanol obtained through biomass has beenproposed as a promising renewable source of hydrogen for these systemsthat address the issue of the greenhouse effect. Furthermore, incountries like Brazil, the use of bio-ethanol has an additionaladvantage since the infrastructure needed for ethanol production anddistribution is already established. However, the hydrogen productionfrom ethanol present some disadvantages such as the formation ofby-products and the deactivation of catalysts [Guil et al., Phys. Chem.B 109 (2005) 10813; Takezawa & Iwasa, Catal. Today 36 (1997) 45;Cavallaro, Mondello & Freni, J. Power Sources 102 (2001) 198]. Anotherproblem related to the use of bio-ethanol is the high costs of ethanolconcentration process from the aqueous solution derived fromfermentation, which contains approximately 10 wt % of ethanol per volumeof solution (H₂O/ethanol molar ratio=23) [Vargas et al, Catal Today 107(2005) 417]. Then, the development of catalysts that exhibit goodperformance under a feedstock containing high H₂O/ethanol molar ratiocould reduce the costs of the use of bio-ethanol as a source of hydrogenfor fuel cells, since the distillation process could be eliminated.

Hydrogen for fuel cells can be produced by steam reforming of alcohols[J. C. Vargas, S. Libs, A. Roger, A. Kiennemann, Catal Today 107 (2005)417, N. Takezawa, N. Iwasa, Catal. Today 36 (1997) 45; S. Cavallaro, N.Mondello, S. Freni, J. Power Sources 102 (2001) 198; J. C. Vargas, S.Libs, A. Roger, A. Kiennemann, Catal Today 107 (2005) 417; N. Takezawa,N. Iwasa, Catal. Today 36 (1997) 45; S. Cavallaro, N. Mondello, S.Freni, J. Power Sources 102 (2001) 198; F J. Marino, E. G. Cerrela, S.Duhalde, M. Jobbagy, M. A. Laborde, Int. J. Hydrogen Energy 12 (1998)1095; F J. Marino, M. Boveri, G. Baronetti, M. Laborde, Int. J. HydrogenEnergy 26 (2001). 665; E. Y. Garcia, M. A Laborde, Int. J. HydrogenEnergy 16 (1991). 3O7; S. Freni, N. Mondello, S. Cavallaro, G. Cacciola,V. N. Parmon, V. A. Sobyanin, React. Kinet. Catal. Lett. 71, (2000)143;V V. Galvita, G. L. Semin, V. D. Belyaev, V. A. Semikolenov, P.Tsiakaras, Sobyanin, Appl. Catal. A: General 220 (2001). 123; A. N.Fatsikostas, D. I. Kondarides, X. E. Verykios, Chem. Commun. 851 (2001);A. N. Fatsikostas, D. I. Kondarides, X. E. Verykios, Catal. Today 75(2002) 145; J. P. Breen, R. Burch, H. M. Coleman, Appl. Catal. B. 39(2002) 65; J. Llorca, N. Horns, J. Sales, P. R. de Ia Piscina, J. Catal209 (2002) 306; J. Comas, F. Marino, M. Laborde, N. Amadeo, Chem. Eng.J., 98 (2004) 61; H. V. Fajardo, L. F. D. Probst, Appl. Catal. A 306(2006) 134; E. G. Wanat, K. Venkataraman, L. D. Schmidt, Appl. Catal. A276 (2004) 155; F. Frusteri, S. Freni, V. Chiodo, L. Spadaro, O. DiBlasi, G. Bonura, S. Cavallaro, Appl. Catal. A 270 (2004) 1] andautothermal reforming of alcohols [Vessellia et al, Appl. Catal. A 281(2005) 13922-26; Navarro et al, Appl. Catal. B, 55 (2005) 229; Velu etal, Catal. Letters 82 (2002) 145; Kugai, Velu & Song, Catal Letters 1012005 255; Deluga et al, Science 303 (2004) 13].

Steam reforming of alcohols like, for example, ethanol (equation 1) isan endothermic reaction. Then, the addition of energy to the system isnecessary, which leads to high capital and operation costs. [A.Haryanto, S. Fernando, N. Murali, S. Adhikari, Energy & Fuels 19 (2005)2098]. One alternative way of supplying heat to the system is to addoxygen or air to the feedstock and simultaneously to burn a portion ofethanol, reaching the thermal neutrality of the reaction [D. K. Liguras,K. Goundani, X. E. Verykios, Int. J. Hydrogen Energy 29 (2004) 419].This process is called autothermal reforming. The autothermal reformingof ethanol is described by the equation 2 [D. K. Liguras, K. Goundani,X. E. Verykios, Int. J. Hydrogen Energy 29 (2004) 419].

C₂H₅OH+3H₂O→2CO₂+6H₂(ΔH°298 =+347.4 kJ/mol)  (1)

C₂H₅OH+0.61O₂+1.78H₂O→2CO₂+4.78H₂(ΔH°298=0 kJ/mol)  (2)

Nevertheless, several parallels reactions can occur on these two routes,depending on the catalysts and the reaction conditions used, hiparticular, for ethanol, the following reactions can be observed:

-   -   (i) Dehydration of ethanol to ethene (equation 3), followed by        polymerization of ethene to form coke (equation 4) [A.        Haryanto, S. Fernando, N. Murali, S. Adhikari, Energy & Fuels        19 (2005) 2098].

C₂H₅OH→C₂H₄+H₂O  (3)

C₂H₄→coque  (4)

-   -   (ii) Decomposition of ethanol (equation 5), producing methane,        carbon monoxide and hydrogen. The methane can react with water        (steam reforming of methane), forming carbon monoxide and        hydrogen (equation 6) [A. Haryanto, S. Fernando, N. Murali, S.        Adhikari, Energy & Fuels 19 (2005) 2098].

C₂H₅OH→CH₄+CO+H₂  (5)

CH₄+H₂O→CO+3H₂  (6)

-   -   (iii) Dehydrogenation of ethanol, producing acetaldehyde        (equation 7) [A. Haryanto, S. Fernando, N. Murali, S. Adhikari,        Energy & Fuels 19 (2005) 2098].

C₂H₅OH→C₂H₄O+H₂  (7)

-   -   (iv) Formation of ketone (equation 8) [T. Nishiguehi, T.        Matsumoto, H. Kanai, K. Utani, Y. Matsumurab, W-J. Shenc, S.        Imamura, Appl. Catal. A 279 (2005) 273]

2C₂H₅OH+H₂O→CH₃COCH₃+CO₂+4H₂  (8)

The appropriated catalyst for reforming of alcohols should maximize thehydrogen production and minimize by-products formation. The majority ofpatents [US 2005/0244329; FR 2 857 003-A1; US 2003/0022950 A1; US2001/0023034 A1; U.S. Pat. No. 6,387,554 B1; FR 2 795 339-A1; WO99/61368; US 2005/0260123 A1; EP 1 314 688 B1; BE 898.686; US2004/0137288 A1] and papers [N. Takezawa, Niwasa, Catal. Today 36 (1997)45; S. Cavallaro, N. Mondello, S. Freni, J. Power Sources 102 (2001)198; J. C. Vargas, S. Libs, A. Roger, A. Kiennemann, Catal Today 107(2005) 417; N. Takezawa, N. Iwasa, Catal. Today 36 (1997) 45; S.Cavallaro, N. Mondello, S. Freni, J. Power Sources 102 (2001) 198; FJ.Marino. E. G. Cerrela, S. Duhalde, M. Jobbagy, M. A. Laborde, Int. J.Hydrogen Energy 12 (1998) 1095; F. J. Marino, M. Boveri, G. Baronetti,M. Laborde, Int. J. Hydrogen Energy 26 (2001). 665; E. Y. Garcia, M. ALaborde, Int. J. Hydrogen Energy 16 (1991). 307; S. Freni, N. Mondello,S. Cavallaro, G. Cacciola, V. N. Parmon, V. A. Sobyanin, React. Kinet.Catal. Lett. 71, (2000)143; V. V. Galvita, G. L. Semin, V. D. Belyaev,V. A. Semikolenov, P. Tsiakaras, Sobyanin, Appl. Catal. A: General 220(2001). 123; A. N. Fatsikostas, D. I. Kondarides, X. E. Verykios, Chem.Commun. 851 (2001); A. N. Fatsikostas, D. I. Kondarides, X. E. Verykios,Catal. Today 75 (2002) 145; J. P. Breen, R. Burch, H. M. Coleman, ApplCatal. B. 39 (2002) 65; J. Llorca, N. Horns, J. Sales, P. R. de IaPiscina, J. Catal 209 (2002) 306; J. Comas, F. Marino, M. Laborde, N.Atnadeo, Chem. Eng. J., 98 (2004) 61; H. V. Fajardo, L. F. D. Probst,Appl. Catal. A 306 (2006) 134; E. C. Wanat, K. Venkataraman, L. D.Schmidt, Appl. Catal. A 276 (2004) 155; F. Frusteri, S. Freni, V.Chiodo, L. Spadaro, O. Di Blasi, G. Bonura, S. Cavallaro, Appl. Catal. A270 (2004)1; E. Vessellia, b, G. Comellia, R. Roseia, S. Frenic, F.Frusteric, S. Cavallaro, Appl. Catal. A 281 (2005) 139; R. M. Navarro,M. C. Alvarez-Galvana, M. C. Sanchez-Sancheza, F. Rosab, J. L. G.Fierro, Appl. Catal. B, 55 (2005) 229; S. Velu, N. Satoh, C. S.Gopinath, K. Suzuki, Catal. Letters 82 (2002) 145; J. Kugai, S. Velu, C.Song, Catal Letters 101 2005 255, G. A. Deluga, J. R. Salge, L. D.Schmidt, X. E. Verykios, Science 303 (2004) 13] found in the literaturereported the use of supported metals as catalysts for steam reformingand autothermal reforming of alcohols. The majority of these catalystsshowed better performance at high temperatures (between 873 and 1023 K).At low temperatures, the production of oxygenated products increases andthe formation of coke is thermodynamically favored. On the other hand,at high temperatures, the thermodynamic equilibrium leads to theproduction of large amounts of CO (higher than 10 ppm), which poison theelectrodes of PEM fuel cells. In order to ensure long and efficient useof hydrogen-fueled PEM fuel cell, highly pure hydrogen must bedelivered. Then, water gas shift reaction and preferential oxidation ofCO reaction or pressure swing adsorption steps are required for COremoval, as showed in FIG. 1.

During the WGS reaction, carbon monoxide is converted to carbon dioxideand hydrogen through a reaction with steam. Although the equilibrium ofthis reaction favors the products formation at lower temperatures,reaction kinetics are faster at higher temperatures [A. Haryanto, S.Fernando, N. Murali, S. Adhikari, Energy & Fuels 19 (2005) 2098]. Then,the water gas shift reaction is carried out in two steps (FIG. 1). Atfirst, the reaction is performed at 623-643 K (high temperature shift—HTS). After this step, the reaction is carried out at 473-493 K (lowtemperature shift—LTS). At the end of the WGS reaction, the COconcentration is between 1.0 and 2.0 mol %. The WGS reaction is followedby preferential oxidation of CO reaction or pressure swing adsorption.The concentration of CO at the exit of this last step is around 10 ppm,which is appropriated to the PEM fuel cells.

Then, the development of the catalysts that exhibit high performance onthe reforming of alcohols at low temperatures, producing low amounts ofCO and by-products, could reduce the costs associated to the hydrogenpurification steps, as described above.

Some works in the literature [J. M. Guil, N, Horns, J. Llorca, P. R. deIa Piscina, J. Phys. Chem. B 109 (2005) 10813; A. Haryanto, S. Fernando,N. Murali, S. Adhikari, Energy & Fuels 19 (2005) 2098; A. N.Fatsikostas, X. E. Verykios, J. Catal 225 (2004) 439; T. Nishiguchi, T.Matsumoto, H. Kanai, K. Utani, Y. Matsumurab, W-J. Shenc, S. Imamura,Appl. Catal. A 279 (2005) 273; N. Laosiripojana, S. Assabumrungrat,Appl. Catal. B 66 (2006) 29; J. Llorca, N. Horns, P. R. de Ia Piscina,J. Catal 227 (2004) 556] showed that the use of oxides as catalysts forsteam reforming and autothermal reforming of alcohols decreases the COformation, which is not detected, depending on the reaction conditionsused. However, when the activity of oxides and supported metal catalystsis compared, it was observed that the former presented lower ethanolconversion than the later. Furthermore, there was a significantformation of by-products such as ethene, acetaldehyde and ketone, overoxides based catalysts.

Al₂O₃ and La₂O₃ oxides exhibited low formation of hydrogen andproduction of large amounts of ethene and acetaldehyde on steamreforming and autothermal reforming of ethanol [A. N. Fatsikostas, X. E.Verykios, J. Catal 225 (2004) 439]. Moreover, it was detected carbondeposition on both oxides, mainly on alumina. The dehydration of ethanoland the dehydrogenation of ethanol reactions were favored over Al₂O₃ andLa₂O₃, respectively.

The performance of CeO₂ on steam reforming of ethanol was evaluated onlyat 593 K [T. Nishiguchi, T. Matsumoto, H. Kanai, K. Utani, Y.Matsumurab, W-J. Shenc, S. Imamura, Appl. Catal. A 279 (2005) 273] andat 1173 K [N. Laosiripojana, S. Assabumrungrat, Appl. Catal. B 66 (2006)29]. It was used a H2O/etanol molar ratio of 5 (593 K) and between 3 and5 (1173 K). In spite of the large amount of catalyst used (450 mg), alow ethanol conversion (˜16%) was obtained at 593K. The main productsobserved were ketone and hydrogen. Moreover, small amounts of ethenewere detected and it was not observed the acetaldehyde formation. Nocomments were done about the stability of this material and theproduction of carbon monoxide during the reaction. At high temperatures(1173 K), CeO₂ oxides with different BET surface areas (22.5 and 7.3m²/g) were studied [N. Laosiripojana, S. Assabumrungrat, Appl. Catal. B66 (2006) 29]. The reaction was carried out at high temperatures sincethe aim of the work was to produce hydrogen for solid oxides fuel cells(SOFCs), which only operate at elevated temperatures. The results showedthat all samples exhibited complete ethanol conversion. Moreover, allcatalysts were stable, when a H₂O/ethanol molar ratio of 3 was used.Concerning the products selectivity, CeO₂ oxide with BET surface area of22.5 m²/g showed the formation of hydrogen, carbon monoxide, carbondioxide and methane. Besides the production of hydrogen, carbonmonoxide, carbon dioxide and methane, small amounts of ethene and ethanewere detected on CeO₂ oxide with lower BET surface area (7 m²/g).Furthermore, for all H₂O/ethanol molar ratios studied, CeO₂ oxide withhigher BET surface area showed the higher hydrogen and carbon monoxideproduction.

The performance of CuO, CuO/SiO₂, CuO/Al₂O₃ and CuO/CeO₂ oxides on steamreforming of ethanol was studied at 473 and 673 K, using a H₂O/ethanolmolar ratio of 5 and 10 [T. Nishiguchi, T. Matsumoto, H. Kanai, K.Utani, Y. Matsumurab, W-J. Shenc, S. Imamura, Appl. Catal. A 279 (2005)273]. Ethanol conversion was higher than 50% for CuO/Al₂O₃ and CuO/CeO₂at temperatures higher than 520 K. Nevertheless, it is important tostress that the performance of these materials was evaluated using largeamounts of catalysts (300-500 mg). Concerning selectivity to products,CuO, CuO/SiO₂ and CuO/Al₂O₃ exhibited low hydrogen formation. Moreover,it was observed a significant amount of acetaldehyde for CuO andCuO/SiO₂ catalysts and a large production of ethene on CuO/Al₂O₃catalyst. In the case of CuO/Al₂O₃, the formation of by-products wasattributed to acid sites of alumina. In order to minimize theby-products production, these sites were neutralized with a KOHsolution. However, the sample treated with KOH presented high productionof acetaldehyde. For CuO/CeO₂ catalyst, hydrogen and ketone were themain products formed. Nevertheless, the hydrogen production was slightlyhigher than that obtained for all catalysts. Acetaldehyde was alsoobserved on CuO/CeO₂ catalyst. According to the authors, theacetaldehyde is produced on CuO and it was converted to ketone on CeO₂.The effect of the addition of MgO to the catalysts was also studied. Theresults showed that the presence of a basic oxide such as MgO, increasedthe formation of ketone and hydrogen. No comments were done about thestability of the catalysts and the production of carbon monoxide duringthe reaction.

According to the literature [J. Llorca, N. Horns, P. R. de Ia Piscina,J. Catal 227 (2004) 556; J. M. Guil, N. Horns, J. Llorca, P. R. de IaPiscina, J. Phys. Chem. B 109 (2005) 10813; J. Llorca, P. R. de IaPiscina, J. Sales, N. Horns, Chem. Commun. (2001) 641], among all oxidesstudied, ZnO presented the best performance on the steam reforming ofethanol at 598-673 K. At this temperature range, the reaction wasperformed using a mixture of water, ethanol and argon(ethanol/H₂O/Ar=1:3:20). The ethanol conversion was low (4.7-15.9%), inspite of the large amounts of catalysts used (300-500 mg). The mainproducts obtained in dry base was hydrogen (45-51%), ethene (˜11-13%),acetaldehyde (˜20-40%) and ketone (˜3-9%). The ethanol conversion washigh only at 673 K, using 100 mg of ZnO and a ethanol/(ethanol+H₂O)molar ratio of 5. Under these conditions, it was observed a highselectivity to hydrogen (61%). However, the formation of by-productssuch as ketone (9.2%), acetaldehyde (5.9%) and ethene (1.9%) was alsodetected. The formation of carbon monoxide was not observed. None of theworks described above evaluated the stability of ZnO on steam reformingof ethanol.

Taking into account the results reported above, it was clear that ahighly active, stable and selective catalysts is still unavailable andit must be developed in order to achieve an efficient process forhydrogen production through steam reforming and autothermal reforming ofalcohols or a mixture of alcohols at low temperatures focused onminimizing the formation of by-products, such as ketone, acetaldehydeand ethene and deplete the CO production.

The catalysts of the present invention exhibited high activity andstability on steam reforming and autothermal reforming of alcohols or amixture of alcohols at low temperatures, providing a process of hydrogenproduction with high selectivity to hydrogen, low formation of carbonmonoxide (<150 ppm), small amounts of acetaldehyde and ethene and noproduction of ketone.

The main goal of this invention is to develop highly active and stablecatalysts, which exhibit high selectivity to hydrogen, without COformation, on steam reforming and autothermal reforming at lowtemperatures of alcohols, in particular ethanol, or a mixture of thesealcohols, like, for example, bio-ethanol. The hydrogen produced is usedas a fuel for a low temperature fuel cell like, for example, PEM fuelcell.

BRIEF DESCRIPTION OF FIGURES

FIG. 1—Scheme of hydrogen production process for PEM fuel cells.

FIG. 2—FIG. 2 shows the ethanol conversion (X_(ethanol)) as a functionof time on stream on steam reforming of ethanol for CeO₂-A catalyst.Reaction conditions: T_(reaction)=773 K; H₂O/etanol molar ratio=2;m_(catalyst)=20 mg; W/Q=0.02 g.s/cm³.

FIG. 3—FIG. 3 presents the ethanol conversion (X_(ethanol)) as afunction of time on stream on steam reforming of ethanol for CeO₂—Bcatalyst. Reaction conditons: T_(reaotion)=773 K; H2O/etanol molarratio=2; m_(catalyst)=20 mg; W/Q=0.02 g.s/cm³.

FIG. 4—FIG. 4 shows the ethanol conversion (X_(ethanol)) as a functionof time on stream on steam reforming of ethanol for Ce_(0.75)Zr_(0.25)O₂catalyst. Reaction conditions: T_(reaction)=773 K; H₂O/etanol molarratio=2; m_(catalyst)=20 mg; W/Q=0.02 g.s/cm³.

DETAILED DESCRIPTION OF THE INVENTION

This invention comprises the use of the cerium oxide based catalystswith or without 0.5-10 wt % of alkaline and alkaline earth promoters(Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra) and mixed oxidescontaining ceria and zirconia and/or yttria an/or lanthanide elements(Ce_(x)M_(1-x)O₂, M=Zr, Y, La, Pr, Nd, Pm, Sm, Eu and 0.1<x<0.9) in thesteam reforming and autothermal reforming at low temperatures ofalcohols, in particular ethanol, or a mixture of these alcohols, like,for example, bio-ethanol. Low temperature was defined as 723-823 K.

The alcohols used in this invention containing one to five carbons (C₁₋₅alcohols), such as, for example, methanol, ethanol, 1-propanol,iso-propanol, 1-butanol, 1-pentanol, or a mixture of alcohols, such as,for example, bio-ethanol. Preferred alcohol is methanol and particularlypreferred is ethanol.

First of all, the preparation of cerium oxide used in the presentinvention is described.

The cerium oxide was obtained by three different methods.

-   -   (1) Method A: Calcination of (NH4)2Ce(NO3)6 in a muffle at        temperatures between 673 an 1273 K, preferably between 700 and        1073 K and more preferably between 723 and 873 K for less than        two hours, preferably for one hour.    -   (2) Method B: Preparation through a method proposed by Chuah et        al [G. K. Chuah, S. Jaenicke, S. A. Cheong, K. S. Chan, Appl.        Catal. A 145 (1996) 267]. At first, an aqueous solution of        cerium (IV) ammonium nitrate and zirconium nitrate was prepared.        Then, it was slowly added to a NH₄OH solution and the pH was        maintained at 10-14, preferably at 11-12. After precipitation,        the material was heated to 323-423 K, preferably between 363 and        373 K, and kept at this temperature for 24-120 hours, preferably        for 72-100 hours. The precipitate was collected by a centrifuge.        Finally, the material was washed until it achieves pH=7 and        dried at 373-423 K, preferably between 383 and 403 K for 8-24        hours, preferably 10-14 hours. Then, the sample was calcined at        10 K/min, preferably less than 5 K/min and more preferably less        than 2 K/min, up to 673-1273 K, preferably 700-1073 K, and more        preferably 723-873 K, for 8-24 hours, preferably 10-14 hours.    -   (3) Method C: Precipitation of (NH₄)₂Ce(NO₃)₆ with urea. An        aqueous solution of (NH₄)₂Ce(NO₃)₆ and urea was heated to        323-423 K, preferably 353-373 K, under stirring and kept at the        final temperature for 20-72 hours, preferably 24-36 hours. The        material was collected by a centrifuge and washed until it        reaches a pH of 7.0. Then, the sample was dried at 363-423 K5        preferably 383-403 K5 for 8-24 hours, preferably 10-14 hours.        Next, it was calcined at 10 K/min, preferably less than 5 K/min        and more preferably less than 2 K/min, up to 673-1273 K5        preferably 700-1073 K5 and more preferably 723-873 K5 for 8-24        hours, preferably 10-14 hours.

The alkaline and alkaline earth promoters were added to the cerium oxideby the incipient wetness impregnation technique using an aqueoussolution containing the precursor salts of alkaline and alkaline earthmetals. Generally, a chloride or a nitrate of alkaline and alkalineearth metal was used as a precursor salt. The amount of alkaline andalkaline earth promoter added was 0.5 to 10 wt %, preferably 1.5 to 5 wt% and more preferably 1.0 to 2 wt %. After impregnation, the sampleswere dried at 363-423 K, preferably 373-393 K for 12-24 hours,preferably 16-20 hours. Then, they were calcined under air at 573-873 K,preferably 623-723 K, for more than 1 hour, preferably for 2 hours.

Ce_(x)M_(1-x)O₂ oxides were obtained by the precipitation method asdescribed by Hori et al. [[CE. Hori, H. Permana, K. Y. Ng Simon, A.Brenner, K. More, K. M. Rahmoeller, D. Belton, Appl. Catal. B 16 (1998)105]. An aqueous solution of ceria, zirconia and/or yttria and/orlanthanide elements precursors was prepared with the desired composition(0.1<x<0.9, preferably 0.25≦x≦0.75). Then, the ceria and zirconium an/oryttria and/or lanthanide hydroxides were co-precipitated by the additionof an excess of ammonium hydroxide. After filtration and washing withdistilled water until the filtrate reaches a pH of 7.0, the samples werecalcined in muffle at 673-1273 K, preferably 700-1173 K, for less than 2hours, preferably for 1 hour.

Next, steam reforming and autothermal reforming of alcohols (C1 to C5),in particular ethanol, or a mixture of these alcohols, like, forexample, bio-ethanol were performed, using the catalysts prepared by themethods described above. The reactions were carried out in a fixed bedreactor at atmospheric pressure for 3-36 hours, preferably 6-30 hours.

Prior to reaction, the catalysts were pretreated at differentconditions, such as: (i) treatment under air at 673-1273 K, preferably700-1173 K, for less than 2 hours, preferably for one hour; (ii)reduction under H2 at 473-873 K, preferably at 523-823 K, for less than2 hours, preferably for one hour.

The reaction temperature is generally 723 to 823 K, preferably 773 K.

The feedstock contained a H2O/alcohol molar ratio between 0 and 15,preferably between 2 and 6.

The oxygen was introduced in the feed in order to have a O2/alcoholmolar ratio of 0.1-5.0, preferably 0.5-1.0.

The residence time used (W/Q; W=mass of catalyst and Q=volumetric flow)was 0.01-0.08 g.s/cm³, preferably 0.015-0.03 g.s/cm³.

All catalysts exhibited good stability and high selectivity to hydrogenin the reaction conditions described above.

The present invention will be described by the following examples, whichare provided for illustrative purposes only.

Example 1 Preparation of CeO2 Catalyst by Method A (CeO2-A)

The CeO₂-A catalyst was obtained through calcination of (NH₄)₂Ce(NO₃)₆at 773 for 1 hour in muffle.

Example 2 Preparation of CeO2 catalyst by Method B (CeO2-B)

An aqueous solution with 10% wt of (NH₄)₂Ce(NO₃)₆) and an aqueoussolution of NH₄OH (5M) were prepared. The solution of (NH₄)₂Ce(NO₃)₆ wasslowly added to the solution of NH₄OH and the pH was adjusted in orderto have an alkaline solution. After precipitation, the material washeated to 369 K and kept at the final temperature for 96 hours. Next,the sample was collected by a centrifuge, washed and dried at 393 K for12 hours. Then, the material was calcined at 1 K/min up to 773 K andkept at this temperature for 12 h.

Example 3 Evaluation of the Stability of CeO₂-A Catalyst on SteamReforming of Ethanol

The stability of CeO₂-A catalyst, which was prepared as described in theexample 1, was evaluated on steam reforming of ethanol for 30 hours timeon stream. The reaction was carried out in a fixed bed reactor atatmospheric pressure. Prior to reaction, the catalyst was reduced underH₂ at 573 K for 1 hour. The reaction was performed at 773 K5 using 20 mgof catalyst and W/Q=0.02 g.s/cm³. The reactants were fed to the reactorby bubbling N2 through two saturators (one of them containing ethanoland the other containing water) in order to obtain an ethanol:H2O:N₂molar ratio=1:2:22.5.

FIG. 2 shows the ethanol conversion (X_(ethanol)) as a function of timeon stream obtained on steam reforming of ethanol for CeO₂-A catalyst.The initial ethanol conversion was, approximately, 77%. It was alsoobserved that, after an initial period of slight deactivation, thecatalyst became practically stable (FIG. 2).

Example 4 Evaluation of the Performance of CeO2-B Catalyst on SteamReforming of Ethanol

The performance of CeO₂—B catalyst, which was prepared as described inthe example 2, was evaluated on steam reforming of ethanol. The reactionwas performed at the same conditions described in example 3.

The ethanol conversion (X_(ethanol)) and the products distribution as afunction of time on stream for CeO₂—B catalyst are presented in FIG. 3.

The initial ethanol conversion was, approximately, 67%. Moreover, theCeO₂—B catalyst exhibited a slight deactivation in the beginning of thereaction, becoming stable after 4 hours time on stream. Hydrogen andcarbon dioxide were the main products obtained. It was also observed theformation of small amounts of acetaldehyde and ethene. Furthermore, onlytraces of carbon monoxide were produced (˜150 ppm) and the formation ofketone was not detected.

Example 5 Preparation of Ce_(0.75)Zr_(0.25)O₂ Catalyst

For the preparation of Ce_(x)M_(1-x)O₂ catalyst with x=0.75 and M=Zr(Ce_(0.75)Zr_(0.25)O₂), an aqueous solution of cerium (IV) ammoniumnitrate and zirconium nitrate was prepared with the Ce/Zr ratio of 3.0.Then, the ceria and zirconium hydroxides were co-precipitated by theaddition of an excess of ammonium hydroxide. After filtration andwashing with distilled water until the filtrate reaches a pH of 7.0, thesample were calcined at 1073 K for 1 hour in a muffle.

Example 6 Evaluation of the Stability of Ce_(0.75)Zro.25O2 catalyst onSteam Reforming of Ethanol

The stability of Ce_(0.75)Zr_(0.25)O₂ catalyst, which was prepared asdescribed in example 5, was evaluated on steam reforming of ethanol for30 hours time on stream. The reaction was carried out in a fixed bedreactor at atmospheric pressure. Prior to reaction, the catalyst wasreduced at 773 K for 1 hour. The reaction was performed at 773 K5 using20 mg of catalyst and W/Q=0.02 g.s/cm³. The reactants were fed to thereactor by bubbling N₂ through two saturators (one of them containingethanol and the other containing water) in order to obtain aethanol:H₂O:N₂ molar ratio=1:3:17.

FIG. 4 shows the ethanol conversion (X_(ethanol)) as a function of timeon stream obtained for Ce_(0.75)Zr_(0.25)O₂ catalyst. The ethanolconversion was complete and the catalyst remained quite stable during 30hours time on stream.

The examples reported above show that the catalysts of the presentinvention exhibit high activity and stability, high selectivity tohydrogen, low formation of carbon monoxide (<150 ppm), small amounts ofacetaldehyde and ethene and no production of ketone.

1. Catalyst for steam reforming and autothermal reforming of alcohols atlow temperature which comprises cerium oxide based materials. 2.Catalyst for steam reforming and autothermal reforming of alcohols atlow temperature according to claim 1 which comprises cerium oxide basedmaterials with or without 0.5-10 wt % of alkaline and alkaline earthpromoters.
 3. Catalyst for steam reforming and autothermal reforming ofalcohols at low temperature according to claim 2 which comprises ceriumoxide based materials with or without 1.5-5.0 wt % of alkaline andalkaline earth promoters.
 4. Catalyst for steam reforming andautothermal reforming of alcohols at low temperature according to claim3 which comprises cerium oxide based materials with or without 1.0-2.0wt % of alkaline and alkaline earth promoters.
 5. Catalyst for steamreforming and autothermal reforming of alcohols at low temperature whichcomprises Ce_(x)M_(1-x)O₂ mixed oxides wherein 0.1<x<0.9 and M=zirconiaand/or yttria and/or elements of lanthanide group.
 6. Catalyst for steamreforming and autothermal reforming of alcohols at low temperatureaccording to claim 5 which comprises Ce_(x)M_(1-x)O₂ mixed oxideswherein 0.1<x<0.9 and M=Zr, Y, La, Pr, Nd, Pm, Sm, Eu.
 7. Catalyst forsteam reforming and autothermal reforming of alcohols at low temperatureaccording to claim 5 which comprises Ce_(x)M_(1-x)O₂ mixed oxideswherein 0.25≦x≦0.75.
 8. Use of the catalysts on steam reforming andautothermal reforming of alcohols at low temperature according to anyone of claims 1 to 7, in the following reaction conditions: (i) reactiontemperature from 723 to 823 K; (ii) H₂O/etanol molar ratio between 0 and15; (iii) O₂/etanol molar ratio between 0.1 and 2.0 and (iv) residencetime (W/Q) of 0.01-0.08 g.s/cm³.
 9. Use of the catalysts on steamreforming and autothermal reforming of alcohols at low temperatureaccording to any one of claims 1 to 7, in the following reactionconditions: (i) reaction temperature of 773 K; (ii) H₂O/etanol molarratio between 2 and 6; (iii) O₂/etanol molar ratio between 0.5 and 1.0and (iv) residence time (W/Q) of 0.015-0.03 g.s/cm³.
 10. Steam reformingand autothermal reforming of alcohols at low temperature, whichcomprises the use of cerium oxide based catalysts according to claims 1,5 and 8 and C₁₋₅ alcohols.
 11. Steam reforming and autothermal reformingof alcohols at low temperature, which comprises the use of cerium oxidebased catalysts according to claim 10, wherein the alcohol is methanol.12. Steam reforming and autothermal reforming of alcohols at lowtemperature, which comprises the use of cerium oxide based catalystsaccording to claim 10, wherein the alcohol is the ethanol.